Take a pill A link between air travel and a higher risk of deep-vein thrombosis (DVT) is widely suspected, but the causes are uncertain. Aviation Health (AH), an independent body dealing with aviation issues, suggests precautionary measures. Unless contraindicated, a low-dose aspirin (100-150mg) taken the day before a flight, on the day and for two or three days after can reduce the risk of pulmonary embolism by up to 60%. Studies at Dokkyo University, Japan, meanwhile, found that a natural protein in fermented soya beans has an anti-thrombotic effect similar to that of the anticoagulant drug heparin - AH recommends NKCP NattoTabs supplements (from healthy.co.uk), and compression socks to prevent blood pooling in the feet and lower legs.

Stay hydrated Relative humidity in the cabin can be anything from 2%-23%, well below the 30%-65% comfort zone; and the fewer passengers on board, the drier the atmosphere. "Dry air hampers the respiratory system's defences, so increasing susceptibility to infection," says Professor Ron Eccles of the Common Cold Centre. He recommends sipping water before and during the flight, to keep sinuses moist and boost their effectiveness at flushing out viruses. And avoid carbonated drinks, says Farrol Kahn, director of AH?: "At altitude, gases in the digestive system can expand by a third, causing abdominal pain." One non-fizzy alcoholic drink before takeoff is fine (to soothe pre-flight nerves), but avoid it on board: alcohol dehydrates and further reduces oxygen supplies to the brain.

Don't be calm Nervous about takeoff ? Hypnotherapist Ursula James (ursulajames.com) says that, on the eve of a flight, you should try to visualise yourself relaxed, walking on to the plane, sitting through the flight, then landing, cool and collected. If pre-flight anxiety surfaces, it helps to imagine a time when you felt eager, but not fearful, anticipation. "Recalling an exciting rather than a calm event works with the physiology of stress," she says. "Anxiety and excitement are identical in physical terms - short breath, butterflies and so on - so changing the psychological overlay from one to the other is easier than trying to force an opposite state such as calm."

Shake a leg Longer check-in times mean you're likely to be waiting in terminals for many hours, most of them seated. Farrol Kahn advises taking a brisk walk at every opportunity, to bolster circulation. Pre-flight exercise will relax you, and also reduce the likelihood of in-flight aches and stiffness. On board, do the anti-DVT exercises that many airlines provide these days. Walk up and down the aisles when you can, too - "Aim for around 15 minutes' movement every hour," Kahn says.

Eat light After a meal, the body diverts oxygenated blood to the gut to help fuel digestion. With up to 25% reduced oxygen on board, eating heavily can strain the body and the digestive system, which will "summon" oxygen from anywhere it can - the brain included - leaving you vulnerable to fainting should you then leave your seat. Instead, snack - lightly. Salads and fruit are good, because they are water-rich, so contribute to hydration, and contain mostly carbohydrates, which are comfortably digested. Avoid gas-producing food such as legumes or brassicas. "It's also important to be hungry when you arrive at your destination, so you can 'fall in' with local meal times," says Kahn. "This helps your body clock adjust to the new time zone."

Keep your hands clean A 2002 study at the University of California found that, of 1,100 passengers flying from San Francisco to Denver, one-fifth reported cold symptoms within a week of arrival. "Every surface of the plane is covered in bacteria and viruses, not just those of your fellow passengers, but those of all the other international passengers who've flown on that plane in the past 24 hours," says the Common Cold Centre's Ron Eccles. He recommends regular use of alcohol-based hand wipes to protect against two of the more common means of disease transmission - into the eye or nose via infections gathered on fingertips.

Adjust yuor sleep patterns A study by the Rush University Medical Centre in the US has revealed a possible strategy for advancing circadian rhythms in preparation for eastward flight by using increased morning light exposure and doses of the sleep-regulating hormone melatonin. Although available as a supplement, melatonin's use for jet lag is not yet approved by the US Food & Drug Administration or endorsed by AH, because side-effects cannot yet be ruled out. Instead, if flying east, "Go to bed early the day before you fly, have a catnap on the plane if you can, and sleep for only 45 minutes maximum if you need to when you arrive," Farrol Kahn advises. And if flying west? You need to rewind your circadian rhythm - the best way is to stay up as late as possible on arrival. Time spent in bright light helps delay the onset of somnolence.